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Tetragonal crystal system

About: Tetragonal crystal system is a(n) research topic. Over the lifetime, 26887 publication(s) have been published within this topic receiving 533609 citation(s). The topic is also known as: tetragonal.

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Abstract: Dielectric properties, lattice‐ and microstructure of ceramic BaTiO3 showing grain sizes of 0.3–100 μm were studied. At grain sizes <10 μm the width of ferroelectric 90° domains decreases proportionally to the square root of the grain diameter. The decreasing width of the domains can be theoretically explained by the equilibrium of elastic field energy and domain wall energy. The smaller the grains, the more the dielectric and the elastic constants are determined by the contribution of 90° domain walls. The permittivity below the Curie point shows a pronounced maximum er ≊5000 at grain sizes 0.8–1 μm. At grain sizes <0.7 μm the permittivity strongly decreases and the lattice gradually changes from tetragonal to pseudocubic.

1,651 citations

Journal ArticleDOI
Abstract: BiVO4 photocatalysts for O2 evolution, which work under visible light irradiation, were prepared by an aqueous process. The BiVO4 photocatalysts were obtained by the reaction of layered potassium vanadate powder (KV3O8 and K3V5O14) with Bi(NO3)3 for 3 days in aqueous media at room temperature. Highly crystalline monoclinic and tetragonal BiVO4 were selectively synthesized by changing the ratio of vanadium to bismuth in the starting materials. X-ray diffraction and scanning electron microscopy measurements showed that the monoclinic BiVO4 was formed via a tetragonal BiVO4 intermediate. Tetragonal BiVO4 with a 2.9 eV band gap mainly possessed an ultraviolet absorption band while monoclinic BiVO4 with a 2.4 eV band gap had a characteristic visible light absorption band in addition to the UV band. The UV bands observed in the tetragonal and monoclinic BiVO4 were assigned to the band transition from O2p to V3d whereas the visible light absorption was due to the transition from a valence band formed by Bi6s or ...

1,628 citations

Journal ArticleDOI
Abstract: Lithium has been inserted chemically and electrochemically into Mn3O4 and Li[Mn2]O4 at room temperature From X-ray diffraction, it is shown that the [Mn2]O4 subarray of the A[B2]X4 spinels remains unperturbed and that the electrons compensating for the Li+-ion charge reduce Mn3+ to Mn2+ in Mn3O4 and Mn4+ to Mn3+ in Li[Mn2]O4 In LixMn3O4, the tetragonal distortion due to a cooperative Jahn-Teller distortion by octahedral-site Mn3+ ions decreases with x from c a = 1157 for x = 0 to c a = 1054 for x = 1 The system Li1+x[Mn2]O4, is cubic at x = 0 and tetragonal ( c a = 1161 ) at x = 12 Electrochemical data reveal a two-phase region in the Li1+xMn2O4 system and a maximum xm = 125 X-ray diffraction confirms the coexistence of a cubic and a tetragonal phase in the compositional range 01 ≤ x ≤ 08 The X-ray data also show that the inserted Li+ ions occupy the interstitial octahedral positions of the spinel structure However, in LixMn3O4 the tetrahedral-site Mn2+ions are displaced from the A positions to the interstitial octahedral positions, as in LixFe3O4, whereas the tetrahedral-site Li+ ions in Li[Mn2]O4 remain on the A sites

1,438 citations

Journal ArticleDOI
Abstract: First principles calculations were performed to investigate the structural, elastic, and electronic properties of IrN2 for various space groups: cubic Fm-3m and Pa-3, hexagonal P3(2)21, tetragonal P4(2)/mnm, orthorhombic Pmmn, Pnnm, and Pnn2, and monoclinic P2(1)/c. Our calculation indicates that the P2(1)/c phase with arsenopyrite-type structure is energetically more stable than the other phases. It is semiconducting (the remaining phases are metallic) and contains diatomic N-N with the bond distance of 1.414 A. These characters are consistent with the experimental facts that IrN2 is in lower symmetry and nonmetallic. Our conclusion is also in agreement with the recent theoretical studies that the most stable phase of IrN2 is monoclinic P2(1)/c. The calculated bulk modulus of 373 GPa is also the highest among the considered space groups. It matches the recent theoretical values of 357 GPa within 4.3% and of 402 GPa within 7.8%, but smaller than the experimental value of 428 GPa by 14.7%. Chemical bonding and potential displacive phase transitions are discussed for IrN2. For IrN3, cubic skutterudite structure (Im-3) was assumed.

1,412 citations

Journal ArticleDOI
Abstract: Lead-free piezoelectric ceramics (1−x)(Na0.5K0.5)NbO3–xLiNbO3 {[Lix(Na0.5K0.5)1−x]NbO3} (x=0.04–0.20) have been synthesized by an ordinary sintering technique. The materials with perovskite structure is orthorhombic phase at x⩽0.05 and becomes tetragonal phase at x⩾0.07, a phase K3Li2Nb5O15 with tetragonal tungsten bronze structure begins to appear at x=0.08 and becomes dominant with increasing the content of LiNbO3. A morphotropic phase boundary between orthorhombic and tetragonal phases is found in the composition range 0.05

1,304 citations

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